This stunning infrared image of Saturn's northern region shows a luminous aurora with the planet's mottled rings below. The aurora appeared in an area that the Hubble Space Telescope can't see, so no one knew it was there until Cassini spotted it recently. What's really weird is that astronomers aren't really sure what's causing it, since this aurora doesn't conform to known models of aurora formation.Most auroras in the solar system, including Earth's, are caused by the interaction between charged particles in the solar wind and a planet's magnetic field. Saturn has a main aurora that is caused by the solar wind. Jupiter has an aurora caused by the interaction of Jupiter's magnetic field and the magnetic properties of its moons. The infrared aurora on Saturn doesn't fit either of those models. University College London astronomer Nick Achilleos, a member of the Cassini team, said, "Trying to explain its origin will no doubt lead us to physics which uniquely operates in the environment of Saturn." Scientists will keep an eye on the phenomena in an effort to find more clues about its nature. So far, the aurora has been observed to be highly variable, shifting in size and even periodically disappearing. Image by: NASA/JPL/University of Arizona.Cassini Finds Mysterious New Aurora On Saturn. [Science Daily]